《Swift从入门到精通》（十三）：反初始化（析构过程）

反初始化（析构过程）

• 类实例销毁之前会立即调用析构器，用关键字 deinit

反初始化（析构过程）如何工作

• Swift仍然使用ARC管理机制，大部分情况下实例销毁不用手动清理；但有些情况下需要自己做一些额外的操作在实例销毁前，此时要可在析构器里实现

• 一个类至多只有一个析构器

  deinit {
      // perform the deinitialization
  }
  
  

• 析构器是自动调用

• 析构调用之后实例才会被销毁，所以在析构器中可以访问实例的所有属性，可以修改这些属性的行为

析构器的运用

    // 示例程序
    class Bank {
        static var coinsInBank = 10_000
        static func distribute(coins numberOfCoinsRequested: Int) -> Int {
            let numberOfCoinsToVend = min(numberOfCoinsRequested, coinsInBank)
            coinsInBank -= numberOfCoinsToVend
            return numberOfCoinsToVend
        }
        static func receive(coins: Int) {
            coinsInBank += coins
        }
    }
    class Player {
        var coinsInPurse: Int
        init(coins: Int) {
            coinsInPurse = Bank.distribute(coins: coins)
        }
        func win(coins: Int) {
            coinsInPurse += Bank.distribute(coins: coins)
        }
        deinit {
            Bank.receive(coins: coinsInPurse)
        }
    }
    var playerOne: Player? = Player(coins: 100)
    print("A new player has joined the game with \(playerOne!.coinsInPurse) coins")
    // Prints "A new player has joined the game with 100 coins"
    print("There are now \(Bank.coinsInBank) coins left in the bank")
    // Prints "There are now 9900 coins left in the bank"
    playerOne!.win(coins: 2_000)
    print("PlayerOne won 2000 coins & now has \(playerOne!.coinsInPurse) coins")
    // Prints "PlayerOne won 2000 coins & now has 2100 coins"
    print("The bank now only has \(Bank.coinsInBank) coins left")
    // Prints "The bank now only has 7900 coins left"
    playerOne = nil
    print("PlayerOne has left the game")
    // Prints "PlayerOne has left the game"
    print("The bank now has \(Bank.coinsInBank) coins")
    // Prints "The bank now has 10000 coins"